Even if you don’t smoke when you’re pregnant, just being around smokers, can increase the risk of harming your future baby, according to a new study in the medical journal Pediatrics.

Researchers found exposure to secondhand smoke increased a non-smoking pregnant woman’s changes of having a stillborn by 23 percent, and increased the risk of delivering a baby with birth defects by 13 percent.

“These results highlight the importance of smoking prevention and cessation focusing on the father in addition to the mother, during the preconception period and during the pregnancy,” explains Dr. Jonathan Winickoff, Associate Professor of Pediatrics at Harvard Medical School, who is not affiliated with the study.

The team of experts reviewed virtually all available studies worldwide that focused on this health issue.

The scientists aren’t exactly sure what levels of secondhand smoke are dangerous, but they do think the more exposure the higher the risks.

“We anticipate that the effect becomes significant when the woman is exposed to more than 10 cigarettes a day, which isn’t a lot when you consider that some women are exposed to partners and other people’s smoking habits on a daily basis. However, we need more evidence to be able to say with certainty what the true levels are,” explains study author Jo Leonardi-Bee, PhD and Associate Professor in Medical Statistics at the University of Nottingham in England.